Diagnostic method for a reagent material to be introduced into an exhaust gas region of an internal combustion engine and device for performing the method

ABSTRACT

The invention relates to a diagnostic method for a reagent to be introduced into an exhaust gas region of an internal combustion engine, or a precursor of the reagent, which is required to convert at least one exhaust gas component in a catalytic converter, and to a device for performing the method. A change in the load of the internal combustion engine is first determined relative to time. If a load change threshold is exceeded, a first release signal is provided. The relative reagent material fill level in the catalytic converter is further determined. If a relative fill level threshold value is exceeded, a second release signal is provided. The reagent material slack occurring downstream of the catalytic converter is compared to a reagent material slack threshold value. If the first and second release signals are present and the reagent material slack threshold value is exceeded, the reagent material is considered to be of sufficient quality.

TECHNICAL FIELD

The invention is based on a diagnostic method for a reagent to be introduced into an exhaust gas region of an internal combustion engine and on a device for performing the method according to the category of the independent claims.

Subject matter of the present invention is also a control unit program as well as a control unit program product.

BACKGROUND

DE 199 03 439 A1 describes a method and a device for operating a combustion engine, in whose exhaust gas region a SCR-catalyzer (selective-catalytic-reduction) is arranged, which reduces the nitrous gases that are contained in the exhaust gas of the combustion engine with a reagent to nitrogen. The metering of the reagent takes place preferably depending on operating parameters of the combustion engine, as for example the engine speed and the injected fuel amount. Furthermore the metering takes preferably place depending on exhaust gas operating parameters such as the exhaust gas temperature or the operating temperature of the SCR-catalyzer.

The reagent ammoniac is for example used as reagent, which can be won from a urea/water solution. The metering of the reagent or the reactant of the reagent has to be determined thoroughly. A metering that is too low causes that nitrous gases cannot be anymore completely reduced in the SCR-catalyzer. A metering that is too high causes a reagent material slack, which can result in unnecessarily high reagent consumption on the one hand and depending on the consistency of the reagent in an undesired odor nuisance. Furthermore it has to be considered that ammoniac is toxic.

DE 10 2004 031 624 describes a method for operating a SCR-catalyzer for purifying the exhaust gas of a combustion engine, at which a control or regulation of the reagent filling level in the SCR-catalyzer with a default storage set value is provided. The targeted default of the storage set value ensures on the one hand that in non-stationary statuses of the combustion engine a sufficient reagent amount is provided for the preferably complete elimination of the NOx-emissions of the combustion engine, and on the other hand that a reagent material slack is avoided. The absolute reagent filling level of the SCR-catalyzer is determined by a catalytic converter model, which considers the NOx-mass flow that flows into the SCR-catalyzer, the NOx-mass flow that leaves the SCR-catalyzer, the catalyzer temperature and if necessary the reagent material slack. The maximally possible reagent filling level of the SCR-catalyzer depends in particular on the operating temperature of the SCR-catalyzer. The maximally possible reagent filling level is the highest at lower operating temperature and decreases with and drops to lower values operating temperature. Therefore the relative reagent filling level, which relates to the maximally possible reagent filling level under the given operating conditions, is considered instead of the absolute reagent filling level.

The reduction of nitrous gases is only possible if the urea/water solution has a default concentration or a certain quality. By contrast, when filling the urea/water solution tank with a urea/water solution of a lower quality or even with a wrong reagent or a precursor of a reagent a reduction of the nitrous gases in the exhaust gas of the combustion unit is not ensured.

DE 10 2006 055 235 A1 describes a diagnostic method for a urea/water solution, at which the signal of an exhaust gas sensor that is arranged downstream after a SCR-catalyzer for determining the nitrogen oxide or ammoniac concentration is compared with a default reference value during a default length of time after filling the urea/water solution tank and if the signal deviates from the reference values by default threshold values a urea/water solution of a lower quality can be assumed.

The invention is based on the task to propose a diagnostic method for a reagent to be introduced into the exhaust gas region of an internal combustion engine as well as a device for performing the method, which is can be simply realized.

The task is solved by the characteristics that are stated in the independent claims.

SUMMARY

The approach of the invention with the characteristics of the independent claim provides the advantage that only downstream after the catalyzer occurring reagent material slacks have to be measured. The steps of the procedure can be performed with available and in a control unit familiar parameters, so that a minimum effort is required.

The approach of the invention enables the detection of the quality of the used reagent. By detecting a bad quality or a wrong reagent a warning notice can take place. The approach according to the invention contributes therefore to guaranteeing a constantly high conversion of undesired components of the exhaust gas of a combustion engine.

Advantageous improvements and embodiments of the invention accrue form dependent claims.

One embodiment provides that in the presence of a first and a second release signal an average value of the occurring and not occurring exceeds of a reagent material slack threshold value is created and that the reagent is associated with a sufficient quality if an average threshold value is exceeded. The certainty of the diagnosis is thereby increased and misdiagnoses due to sporadic events or interfering signals are avoided.

The device according to the invention for performing the method concerns first a control unit, which has customized means for implementing the procedure. The control unit preferably contains at least one electrical storage, in which the steps of the procedure are saved as control unit program.

The control unit contains a reagent filling level detection for detecting the relative reagent filling level, load change detection for detecting a change of the load of the combustion engine in relation to the time as well as a reagent material slack comparator for comparing the reagent material slack with a reagent material slack threshold value.

One embodiment of the device according to the invention provides a NOx-sensor as the exhaust gas sensor, which has a cross sensitivity towards the reagent. Alternatively a sensor can be provided as the exhaust gas sensor, whose sensitivity towards the reagent is specially arranged. As long a urea/water solution is provided as the reagent, from which the reagent ammoniac is won, a NH3-sensor can be provided as exhaust gas sensor.

The control unit program according to the invention provides that all steps of the procedure are performed when it runs in the control unit.

The control unit program product according to the invention with a program code that is saved on a machine readable device performs the procedure, if the program runs in the control unit.

Further advantageous improvements and embodiments of the procedure according to the invention arise from further dependent claims. Embodiments of the invention are illustrated in the drawing and further explained in the subsequent description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a technical environment, in which the procedure according to the invention is carried out;

FIGS. 2 a-2 g each show a signal course depending on the time.

DETAILED DESCRIPTION

FIG. 1 shows a combustion engine 10, in whose exhaust gas region 11 a reagent introducing device 12, a catalyzer 13 as well as an exhaust gas sensor are arranged. A NOx-concentration % NOx_vK occurs upstream in front of the catalyzer 13 and a reagent material slack % NH3_nK downstream after the catalyzer 13.

The reagent introducing device 12 is assigned to a metering valve DV, which is impinged by a control unit 20 with a metering signal s_D. the exhaust gas sensor 14 provides a reagent material slack measuring signal NH3_Mes to the control unit 20.

The exhaust gas of the combustion engine 10 contains at least one undesired exhaust gas component, which the catalyzer has to reduce. Such an undesired exhaust gas component is for example the NOx-concentration % NOx_vK, which has to be converted in the catalyzer 13 into less harmful connections. It is assumed that the catalyzer 13 requires a reagent for the conversion, which is introduced into the exhaust gas upstream before the catalyzer 13. The reagent can be introduced for example inside the motor itself. In the shown embodiment it is assumed that the reagent is dosed into the exhaust gas over the reagent introducing device 12. The reagent amount is determined by the metering valve DV, which is impinged with the metering signal s_D. the metering signal s_D is determined by the control unit 20 preferably with the aid of familiar operating parameters of the combustion engine 10 such as the engine speed or the load La.

The position of a not further shown accelerator pedal for example can be used as a measure for the load La of the combustion engine 10, as long as the combustion engine 10 is provided as the drive in a motor vehicle. Furthermore a torque provided by the combustion engine 10 can be used as a measure for the load La. Additionally the air amount that is added to the combustion engine 10 and/or an exhaust gas recirculation rate can be considered.

It is assumed in the shown embodiment that the catalytic converter 13 is arranged as SCR-catalyzer, which converts the NOx-parts of the exhaust gas with the reagent ammoniac. The ammoniac can for example be won from a urea/water solution as precursor of the reagent by a thermal decomposition in the exhaust gas region 11, whereby the urea/water solution is sprayed into the exhaust gas region 11 over the reagent introducing device 12.

In order to achieve a preferably high conversion rate it is necessary that the reagent, in the shown embodiment the urea/water solution, provides a certain consistency. The urea/water solution is for example assumed to be a 32% urea/water solution. The desired conversion rate cannot be reached anymore, if the water percentage is either accidentally or deceitfully increased, or if a completely wrong reagent is used, so that statutory provisions for the exhaust gas purification are not fulfilled anymore.

The procedure according to the invention provides therefore a diagnosis of the reagent or a precursor of the reagent that has to be introduced into the exhaust gas region 11 of the combustion engine 10. The diagnosis is based on the fact, that a reagent material slack occurs % NH3_nK, which is detected by the exhaust gas sensor 14 and provided as reagent material slack measuring signal NH3_Mes to the control unit 20, at a higher reagent filling level in the catalyzer 13, which can store the reagent, and at a simultaneously occurring load change of the combustion engine 10, which results in an increase of the metering of the reagent. If such a reagent material slack % NH3_nKcannot be detected under the mentioned conditions and if the components of the entire exhaust gas purification system are alright apart from that, it can be assumed, that a wrong of insufficient reagent or precursor of the reagent has been introduced into the exhaust gas region 11.

First a load change of the combustion engine 10 is detected. The time course of the load La is shown in FIG. 2 a, whereby it is assumed that the diagnostic method begins at a later point of time ti1. A load change detection 30 is provided with the load La, the time ti as well as a load change threshold value dLa/dt_Lim. The load change detection 30 determines a timely load change preferably with the aid of the difference quotient of the load La. FIG. 2 b shows the load change signal dLa/dt depending on the time ti. It is assumed that the load change signal dLa/dt exceeds the load change threshold value dLa/dt_Lim at a third point of time ti3, so that a first release signal FG1 is provided by the load change detection 30 at the third point of time ti3. The first release signal FG1 can be calculated from applied engine maps of the initial parameters of the load change detection 30.

It is assumed that with the occurrence of the first release signal FG1 a corresponding increase of the metering of the reagent takes place, whereby an overdosing of the reagent can occur with regard to the storage capacity of the catalyzer 13, which results in an increased reagent material slack % NH3_nK. However a strong advance of the reagent material slack % NH3_nK occurs only if the storage capacity of the catalyzer 13 is mostly exhausted before the increase of the metering.

Therefore it is furthermore provided to determine the relative reagent filling level % FS in the catalyzer 13 in a reagent filling level determination 32, which is provided the NOx-concentration % NOx_vK, the temperature te_Kat of the catalyzer 13 and the metering signal s_D. The determination of the relative reagent filling level % FS can be taken in detail from the initially mentioned state of the art according to DE 10 2004 031 624 A1, which is clearly referred to.

The determination of the relative reagent filling level % FS instead of the absolute reagent filling level is in particular practical because the reagent storage capability of a SCR-catalyzer 13 strongly depends on the temperature, whereby a specific absolute reagent filling level at a low catalyzer temperature te_Kat corresponds with a comparably low relative reagent filling level % FS and at a high catalyzer temperature te_Kat with a comparably high relative reagent filling level % FS. FIG. 2 d shows a possible course of the relative reagent filling level % FS, whereby a relative reagent filling level threshold value % FS_Lim is registered, which is exceeded at a second point of time ti2. In a filling level comparator 34 the relative reagent filling level % FS is compared to the relative reagent filling level threshold value % FS_Lim. The filling level comparator 34 provides a second release signal FG2, when the relative reagent filling level % FS exceeds the relative reagent filling level threshold value % FS_Lim. The second release signal FG2 can be calculated from applied engine maps of the initial parameters of the filling level comparator 34. The relative filling level threshold value % FS_Lim is thereby for example determined to at least 70%. The exceeding of the relative filling level threshold % FS_Lim occurs according to FIG. 2 d at the second point of time ti2 and causes the provision of the second release signal FG2 according to FIG. 2 e.

The provided detection and evaluation of the regent material slack % NH3_nK is based on the fact that an overdosing of the reagent can be assumed at a present first and second release signal FG1, FG2. A reagent material slack comparator 36 compares the reagent material slack measuring signal NH3_Mes with a reagent material slack threshold value NH3_Lim, whereby the reagent material slack comparator 36 provides a first evaluation signal B1, when the reagent material slack measuring signal NH3_Mes exceeds the reagent material slack threshold value NH3_Lim. The reagent material slack measuring signal NH3_Mes along with the reagent material slack threshold value NH3_Lim are shown in FIG. 2 f, whereby the exceeding of the reagent material slack threshold value NH3_Lim occurs at a fourth point of time ti4. The exceeding causes according to FIG. 2 g the provision of the first evaluation signal B1 at the fourth point of time ti4.

Due to the dynamic processes in the catalyzer 13 as well as due to the duration of the exhaust gas in the exhaust gas region 11 a small delay time ti_V is planned preferably between the third and the fourth points of time ti3, ti4. The delay time ti_V is provided to the reagent material slack comparator 36.

The occurrence of the first evaluation signal B1 means that an expected reaction occurred, so that is can be assumed that the reagent has a default quality. As long as no first evaluation signal B1 occurs despite the presence of the two release signals FG1, FG2, it has to be assumed that the reagent or the precursor of the reagent has no sufficient quality or even that a wrong reagent has been used.

In order to increase the accuracy of the diagnostic method according to the invention it can be provided according to an embodiment that not each occurrence of the first evaluation signal B1 or a corresponding absence of the first evaluation signal B1 is used for a direct statement about whether the reagent is of sufficient quality or not. An average value comparator 38 is therefore provided, which is provided with the first evaluation signal B1, the first and second release signal FG1, FG2 as well as an average threshold value BM_Lim. The average value comparator 38 provides a second evaluation signal B2, when an average value of the occurrence or the absence of the first evaluation signal B1 exceeds the average value threshold BM_Lim. When the second evaluation signal B2 occurs it is assumed that a sufficient quality of the reagent has been present.

According to another embodiment it is provided that the reagent threshold value NH3_Lim depends on the load La of the combustion engine 10 and/or on the relative reagent filling level % FS. A reagent material slack threshold determination 40 contains for example engine maps by which the relation is determined. 

1-10. (canceled)
 11. A method of introducing a reagent, or a precursor of the reagent, into an exhaust gas region of an internal combustion engine to convert at least one exhaust gas component in a catalytic converter, the method comprising: determining a change in a load of the internal combustion engine with respect to time, wherein a first release signal is provided if a load change threshold is exceeded; determining a relative reagent fill level in the catalytic converter, wherein a second release signal is provided if a relative fill level threshold value is exceeded; and comparing a measured reagent material slack occurring downstream of the catalytic converter to a reagent material slack threshold value, wherein the reagent is considered to be of sufficient quality if the first and second release signals are provided and the measured reagent material slack exceeds the reagent material slack threshold value.
 12. A method according to claim 11, further comprising creating, upon provision of the first and the second release signal, an average value of the reagent material slack threshold value based on the number of times the measured reagent material slack exceeds the reagent material slack threshold value and number of times the measured reagent material slack does not exceed the reagent material slack threshold value, wherein the reagent is assigned with a sufficient quality if the average value exceeds an average threshold value.
 13. A method according to claim 11, further comprising postponing the comparing of the measured reagent material slack occurring downstream of the catalytic converter by a delay time calculated after the last of the first and second release signals is provided.
 14. A control unit configured to implement, a method of introducing a reagent, or a precursor of the reagent, into an exhaust gas region of an internal combustion engine to convert at least one exhaust gas component in a catalytic converter, the method comprising: determining a change in a load of the internal combustion engine with respect to time, wherein a first release signal is provided if a load change threshold is exceeded; determining a relative reagent fill level in the catalytic converter, wherein a second release signal is provided if a relative fill level threshold value is exceeded; and comparing a measured reagent material slack occurring downstream of the catalytic converter to a reagent material slack threshold value, wherein the reagent is considered to be of sufficient quality if the first and second release signals are provided and the measured reagent material slack exceeds the reagent material slack threshold value.
 15. The control unit of claim 14, wherein the control unit comprises: a load change detection for determining a change of a load of the combustion engine with respect to time; a reagent filling level detection for determining the relative reagent filling level; a filling level comparator for comparing the relative reagent filling level in the catalytic converter with a relative filling level threshold value; and a reagent material slack comparator for comparing a reagent material slack with the reagent material slack threshold value.
 16. The control unit of claim 14, wherein a NOx-sensor is further provided as an exhaust gas sensor that has a cross sensitivity towards the reagent.
 17. The control unit of claim 14, wherein a NH3-sensor is further provided and used as an exhaust gas sensor.
 18. The control unit of claim 14, wherein a urea/water solution is provided as the reagent.
 19. A control unit program that executes, if the program runs on a control unit, the steps of a method of introducing a reagent, or a precursor of the reagent, into an exhaust gas region of an internal combustion engine to convert at least one exhaust gas component in a catalytic converter, the method comprising: determining a change in a load of the internal combustion engine with respect to time, wherein a first release signal is provided if a load change threshold is exceeded; determining a relative reagent fill level in the catalytic converter, wherein a second release signal is provided if a relative fill level threshold value is exceeded; and comparing a measured reagent material slack occurring downstream of the catalytic converter to a reagent material slack threshold value, wherein the reagent is considered to be of sufficient quality if the first and second release signals are provided and the measured reagent material slack exceeds the reagent material slack threshold value, and further comprising creating, upon provision of the first and the second release signal, an average value of the reagent material slack threshold value based on the number of times the measured reagent material slack exceeds the reagent material slack threshold value and number of times the measured reagent material slack does not exceed the reagent material slack threshold value, wherein the reagent is assigned with a sufficient quality if the average value exceeds an average threshold value, and further comprising postponing the comparing of the measured reagent material slack occurring downstream of the catalytic converter by a delay time calculated after the last of the first and second release signals is provided.
 20. A control unit program product with a program code that is stored on a machine readable device to implement, if executed in a control unit, a method of introducing a reagent, or a precursor of the reagent, into an exhaust gas region of an internal combustion engine to convert at least one exhaust gas component in a catalytic converter, the method comprising: determining a change in a load of the internal combustion engine with respect to time, wherein a first release signal is provided if a load change threshold is exceeded; determining a relative reagent fill level in the catalytic converter, wherein a second release signal is provided if a relative fill level threshold value is exceeded; and comparing a measured reagent material slack occurring downstream of the catalytic converter to a reagent material slack threshold value, wherein the reagent is considered to be of sufficient quality if the first and second release signals are provided and the measured reagent material slack exceeds the reagent material slack threshold value, and further comprising creating, upon provision of the first and the second release signal, an average value of the reagent material slack threshold value based on the number of times the measured reagent material slack exceeds the reagent material slack threshold value and number of times the measured reagent material slack does not exceed the reagent material slack threshold value, wherein the reagent is assigned with a sufficient quality if the average value exceeds an average threshold value, and further comprising postponing the comparing of the measured reagent material slack occurring downstream of the catalytic converter by a delay time calculated after the last of the first and second release signals is provided. 